Minimum Number of Operations to Make (#2870)

lcpy gen -n 2870   # by problem number
lcpy gen -s minimum_number_of_operations_to_make_array_empty   # by problem name

Input: nums = [2,3,3,2,2,4,2,3,4]
Output: 4
Explanation: We can apply the following operations to make the array empty:
- Apply the first operation on the elements at indices 0 and 3. The resulting array is nums = [3,3,2,4,2,3,4].
- Apply the first operation on the elements at indices 2 and 4. The resulting array is nums = [3,3,4,3,4].
- Apply the second operation on the elements at indices 0, 1, and 3. The resulting array is nums = [4,4].
- Apply the first operation on the elements at indices 0 and 1. The resulting array is nums = [].
It can be shown that we cannot make the array empty in less than 4 operations.

Input: nums = [2,1,2,2,3,3]
Output: -1
Explanation: It is impossible to empty the array.

from collections import Counter


class Solution:
    # Time: O(n)
    # Space: O(n)
    def min_operations(self, nums: list[int]) -> int:
        operations = 0
        for count in Counter(nums).values():
            if count == 1:
                return -1
            groups, remainder = divmod(count, 3)
            operations += groups + (1 if remainder else 0)
        return operations